Common milkweed (Asclepias syriaca)

Aug. 1, 2012

Common milkweed / Missouri Department of Conservation

Written by

Missouri Department of Conservation

Claim to fame: As the interest in butterfly gardening grows, so does the popularity of common milkweed. This plant’s symbiotic relationship to the monarch butterfly has made this native wildflower a favorite of people who like to see this orange-and-black insect flutter in their yards each summer.

Species status: Common milkweed is abundant throughout most of Missouri.

First discovered: One of the earliest descriptions of common milkweed comes from Canadensium plantarum historia, a description of Canadian plants written by French physician Jacques Philippe Cornut in 1635. Carl Linnaeus used this plant book as a source for writing his taxonomic description of the plant in the 18th century.

Family matters: Common milkweed belongs to the plant family Asclepiadaceae. A common trait of the approximately 2,000 species of herbs and shrubs in this group is milky sap.

Height: As tall as 5 feet.

Flowers: Common milkweed has small pinkish-white flowers arranged in large rounded clusters at the tops of the stems and just below the tops of the stems. Each flower is about a quarter-inch in diameter with five reflexed petals (“reflexed” means the petals curve or bend backward). These petals surround five hoodlike appendages, each hood having a tiny pointed “horn” rising from it.

Seeds/fruits: Fruits are pods that are up to 4 inches long. Each pod is filled with small dark brown seeds; each seed is attached to a tuft of silky hair.

Distinguishing characteristics: Besides the large flower clusters and, later in summer, the pods bearing the “hairy” seeds, another identifying characteristic of a milkweed plant is the thick, leathery leaves that are long (up to 8 inches) and are arranged opposite each other on the stem. The stem is unbranched and has fine hairs. Tearing away the leaves will cause milky sap to ooze from the opening — hence the name “milkweed.”

Annual/biennial/perennial: Common milkweed is a perennial.

Life cycle: After flowering, the plant produces seed pods that dry and open. Wind is the primary agent of dispersal of seeds.